Magnetic recording media are widely used as the recording media of all sorts of data such as audios, images and letters. In recent years, the requirements for high density recording have risen in correspondence with the increment of the capacity of data to be recorded and the improvement of transfer rate, and magnetic recording media having high electromagnetic characteristics are wanted. Further, the reliability in the repeating use of a medium is also required at the same time. Therefore, running properties have been improved by providing a back coat layer, in particular in a tape medium. For improving running properties by a back coat layer, providing protrusions on the base surface to roughen the surface of a back coat layer to thereby improve the running durability has been conventionally tried. However, when the surface of a back coat layer is too roughened by this method, the back coat layer and the magnetic layer are tightly pressed in winding the magnetic recording tape on a hub for the purpose of storage or process, and so-called “imprinting of back coat” occurs, i.e., the magnetic layer is infected with the unevenness of the back coat layer, which results in the reduction of electromagnetic characteristics. For solving the problem of imprinting of back coat, smoothing the surface of a back coat layer has been tried. However, when a back coat layer is smoothed, the air entrained by winding is difficult to come out, as a result irregular winding such as protrusion of the tape is liable to occur. When irregular winding occurs, a tape edge is woven by being brought into contact with the flange of the controlling guide during running of the tape that generates the increment of dropout. The thickness of a magnetic tape is thinned in recent years, so that the problem of weaving of an edge has become serious.
As the conventional example of a trial to better electromagnetic characteristics by smoothing a back coat layer to thereby improve so-called imprinting of back coat (back imprinting), an example of a back coat layer mainly comprising the mixture of granular titanium oxide and carbon black is disclosed in JP-A-11-259851 (The term “JP-A” as used herein refers to an “unexamined published Japanese patent application”.). JP-A-11-259851 also proposes the use of acicular nonmagnetic powder. However, the back coat layer becomes smooth and imprinting of back coat certainly reduces by using these powders, but the back coat layer becomes too smooth and the friction coefficient increases, as a result, the tension during running rises, which results in the increase of dropout. With respect to supports, JP-A-7-6351 and JP-A-8-45060 disclose the molecular weights and viscosities. Both literatures disclose that high edge can be prevented by using polyester-2,6-naphthalate (hereinafter sometimes referred to as “PEN”) having a molecular prescribed to 8,000 to 16,000 or PEN having a viscosity prescribed to 0.45 to 0.53, but these supports are not provided with the back coat layer prescribed in the present invention, so that these are insufficient to achieve high durability. Thus, a magnetic recording tape can not satisfy both of electromagnetic characteristics and the restraint of weaving of an edge by conventional techniques. In particular, in these days when it is required to thin the thickness of a magnetic recording tape as a whole, although a magnetic recording tape having good electromagnetic characteristics and edge quality is required, such a magnetic recording tape is not provided yet.